1. Field of the Invention
The present invention relates generally to a system and method for using a pneumatic line to automate the launch of a cement plug or multiple cement plugs from a cement head. The system ensures that the proper sequence of opening and closing valves in combination with the removal of a retaining device is done to safely launch a cement plug. The present invention discloses varying the pressure in a single pneumatic line to launch multiple cement plugs from a cement head. A wireless remote may be used to regulate the pressure in the pneumatic line to launch cement plugs from the cement head as desired from a remote location.
2. Description of the Related Art
Oil and gas wells typically include steel casing or steel tubing, hereinafter steel casing, cemented into the wellbore to provide support to the wellbore and prevent the wellbore from collapsing. The cement casing is important to support the wellbore formation as well as to help protect the steel casing from being damaged. The first process in creating an oil or gas well is to drill the wellbore or at least a portion of the wellbore. The industry typically uses drilling mud to aid in the drilling process to remove the drill cuttings from the wellbore. The drilling mud typically remains in the wellbore until displaced during the cementing process.
After the wellbore has been drilled to the desired depth, the drilling apparatus is removed and steel casing is inserted into the wellbore. Cement slurry is then pumped into the interior of the casing to cement in the steel casing. The cement slurry flows up in the annulus outside the casing up to a desired level. The cement slurry displaces the drilling mud present in the wellbore and the drilling mud is circulated out of the well. The hardened cement provides support to the wellbore formation as well has helping to protect the steel casing from being damaged. Further, the cement prevents the migration of formation fluids.
During the cementing process it is important to prevent the contamination of the cement slurry with the drilling mud. A cement plug may be launched ahead of the cement slurry. The cement plug helps to separate the cement slurry from the drilling mud present in the wellbore. A second cement plug may be launched after the injection of the cement slurry to help prevent possible contamination of the cement. The cement plugs may be drilled out once the cement casing has hardened in the annulus between the steel casing and the formation.
A cement head is generally attached to the top of the casing to facilitate the cementing of the casing. The cement head generally includes a chamber that holds one or more cement plugs inside the cement head. A retaining device, such as a pin, may be inserted into the cement head to prevent the cement plugs from prematurely exiting the cement head. The cement head also includes ports generally located above and below each plug within the cement head. The port below a plug allows material to be pumped into the well prior to launching the plug into the wellbore while the port above a plug allows material to be pumped into the chamber causing the plug to be launched out of the cement head into the wellbore. The cement head generally includes valves that may be used to open or close the ports in the cement head. The cement head may include a various number of cement plugs and configurations, but for illustrative purposes, a cement head containing a first plug, a second plug, and three ports having valves will be discussed below.
The first port of the cement head is located below the first plug and allows material, such as drilling mud, to be pumped into the wellbore prior to launching the first plug. After it is no longer necessary to pump the drilling mud into the wellbore the device retaining the plug may be removed, the valve to the second port may be opened, and the valve to the first port may be closed. The second port may be located below a second plug and above the first plug. With the second port being open, material such as cement slurry may be pumped into the cement head. The cement slurry above the first plug causes the first plug to be launched into the wellbore. The first plug may act as a spacer between the first material pumped into the wellbore and the cement slurry pumped above the first plug. Cement slurry may be pumped through the second port until a sufficient amount of cement slurry has been pumped to complete the desired cementing process.
After enough cement slurry has been pumped into the wellbore, the device retaining the second plug may be removed or released, the valve to a third port located above the second plug may be opened, and the valve to the second port may be closed. Material may be pumped into the cement head above the second plug causing the second plug to be launched into the wellbore, the second plug may act as a spacer between the cement in the wellbore and the material pumped in above the second plug.
To launch a cement plug, an operator has to manually actuate the valves and remove or release the retaining device as described above. This can be a potentially unsafe activity as the cement head is often located on a derrick high above the wellhead. The cement head is often located in an area considered a zone zero in some regions, such as the North Sea, which is considered hazardous due to the possibility of combustible gases being present. The location of the cement head in a zone zero prevents the use of an electrical device to actuate the valves or manipulate the retaining devices because a spark from the electrical device could ignite combustible gas that may be present.
It would be beneficial to provide a system or apparatus that may be used to remotely launch a cement plug from the cement head, but the location of the cement head in a zone zero may prevent the use of an electrical device to launch the cement plug. One potential solution would be to use a pneumatic system to actuate the cement head valves and to remove the retaining devices. However, such a system may be too cumbersome and complex if a pneumatic line needs to be connected to each valve and each retaining device of the cement head.
The manual operation of the cement head may also be potentially hazardous if the valves and the releasing of the retention device are not operated properly. For example, cement slurry is often pumped into the cement head at a high pressure. The launching of a cement plug requires that two valves and a retaining device be actuated in a proper sequence as discussed above. The premature closure of a valve or failure to remove the retaining device may cause an accident to occur because of the high pressure slurry being pumped into the cement head. Thus, it would be beneficial to provide a system that automates the launching of the cement head ensuring that the valves and retention devices are operated in the proper sequence.
In light of the foregoing, it would be desirable to provide a system that can launch cement plugs from a cement head from a remote location. It would be further desirable to provide a system that prevented the premature opening of a valve or removal of a retaining device prior to launching a cement plug. It would also be desirable to provide a pneumatic system that only required a single pneumatic line to launch multiple cement plugs from a cement head. It would be further desirable to provide a system that automated the launching of cement plugs from a cement head.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.